CN107076406B

CN107076406B - Microfluidic-based apparatus and method for liquid evaporation

Info

Publication number: CN107076406B
Application number: CN201580056901.5A
Authority: CN
Inventors: C·D·梅恩哈特; B·皮奥雷克; N·B·朱迪
Original assignee: Digital Tsukito Design Inc
Current assignee: Digital Tsukito Design Inc
Priority date: 2014-10-20
Filing date: 2015-10-16
Publication date: 2019-12-13
Anticipated expiration: 2035-10-16
Also published as: US20230214550A9; US11821623B2; US20200173648A1; US11408607B2; JP6748075B2; JP2017538399A; US10502409B2; EP3209945A1; US20240191870A1; US20160138795A1; US20230086810A1; WO2016064684A1; CN107076406A

Abstract

A method and apparatus for evaporating a liquid into an ambient environment, comprising: directing liquid from a liquid source to an evaporation port, wherein the evaporation port varies in lateral dimension from 10 μm to 300 μm; applying heat to the liquid in the evaporation port with at least one heating element positioned in thermal communication with the evaporation port; and releasing the vaporized liquid from the vaporization port into the ambient environment to transport the fluid throughout the depth of the structure.

Description

Microfluidic-based apparatus and method for liquid evaporation

Cross Reference to Related Applications

This application claims priority to U.S. provisional application serial No. 62/066320 filed on month 20 of 2014 and serial No. 62/081476 filed on month 18 of 2014, which are incorporated herein by reference in their entirety.

Technical Field

The present description relates to an apparatus and method for vaporizing liquids, and in particular to a vaporizer that provides a well controlled vapor space distribution, has a controlled and precise amount of vapor, has a well controlled vaporization temperature distribution, and has high thermodynamic efficiency.

Background

Vaporizers such as electronic cigarettes, humidifiers, and other personal as well as medical and fragrance vaporizers are becoming more and more common. Many such evaporators rely on technology that has been popular for many years. Such evaporators can benefit from new design methods and modern manufacturing capabilities.

Disclosure of Invention

In some embodiments, the apparatus may be microfabricated using batch fabrication techniques to fabricate the devices to be nearly identical from device to device. Microfabrication allows for the fabrication of devices in large numbers with high unit-to-unit reproducibility and low unit cost.

In some embodiments, there may be provided an evaporation apparatus positionable within an ambient environment to evaporate a liquid into the ambient environment, comprising: at least one liquid source; at least one evaporation port that can be formed in the structure, that has a lateral dimension from 10 μm to 300 μm, and that can be in fluid communication with a source of liquid and an ambient environment; and at least one heating element that may be in thermal communication with the at least one evaporation port.

In some embodiments, fluid communication between the liquid source and the surrounding environment may occur throughout the depth of the apparatus, such that fluid is delivered throughout the depth of the structure.

In some embodiments, the structure may include a thin structured region having a thickness ranging from 1 μm to 100 μm, and in some embodiments from 10 μm to 100 μm.

In some embodiments, a protective layer may be formed on the structure surrounding the heating element.

In some embodiments, the protective layer may comprise deposited glass.

In some embodiments, a surface coating may be formed on the structure, but it may be masked to prevent formation on the walls of the evaporation port.

In some embodiments, the surface coating may comprise a fluoropolymer.

In some embodiments, the surface coating may comprise silicon nitride.

In some embodiments, at least one of the bead or particle wicking structures may be located in at least one of the liquid source regions of the structure or within a port.

In some embodiments, at least one of the beads or particles may have a size of 10 μm to 300 μm or a size of at most 1 mm.

In some embodiments, at least one of the beads or particles may include a hydrophilic surface.

In some embodiments, at least one of the beads or particles may include a hydrophobic surface.

In some embodiments, at least one of the beads or particles may be sintered.

In some embodiments, at least one of the beads or particles is comprised of glass.

In some embodiments, the heating element may be a thin film resistive heating element.

In some embodiments, the resistance of the resistive heating element may be varied to provide a controlled thermal profile.

In some embodiments, the resistive heating elements may be electrically connected in parallel and series combinations.

In some embodiments, there may be provided a method for evaporating a liquid into an ambient environment, comprising: directing the liquid from the liquid source to an evaporation port, wherein the evaporation port may have a lateral dimension ranging from 10 μ ι η to 300 μ ι η; applying heat to the liquid in the evaporation port with at least one heating element located in the vicinity of the evaporation port; and releasing the vaporized liquid from the vaporization port into the ambient environment.

In some embodiments, during operation, liquid may continuously flow from the liquid source to the evaporation port, may change from a liquid phase to a vapor, and vapor may continuously flow from the evaporation port to the ambient environment.

In some embodiments, the fluid may flow from the liquid source to the ambient environment through the depth of the structure.

In some embodiments, the thin structural region can substantially confine thermal energy to the vicinity of the at least one heating element and the at least one evaporation port.

In some embodiments, the thin structural region can reduce thermally induced stresses that may occur near the at least one heating element and the at least one evaporation port.

Drawings

Various aspects and advantages of the embodiments provided herein are described with reference to the following detailed description in conjunction with the accompanying drawings. Throughout the drawings, reference numerals may be reused to indicate correspondence between referenced elements. The drawings are provided to illustrate exemplary embodiments described herein and are not intended to limit the scope of the present disclosure.

Fig. 1 shows a perspective view of an apparatus of an illustrative embodiment.

Fig. 2a and 2b show exploded and cross-sectional views of an illustrative embodiment.

Fig. 3a and 3b show an overview and perspective view of an illustrative embodiment.

Fig. 4a, 4b and 4c show overview views of an apparatus depicting components of an illustrative embodiment.

FIG. 5 shows a top view of an apparatus depicting some of the major components of an illustrative embodiment.

Fig. 6a and 6b show schematic diagrams of an exemplary microfluidic evaporation chip of an illustrative embodiment containing 18 evaporation clusters.

Fig. 7a and 7b show an example of a micro-fabrication process flow for device fabrication of the illustrative embodiments.

FIG. 8 shows a flowchart depicting a method of an illustrative embodiment.

FIG. 9 shows an overview of an apparatus depicting the major components of an illustrative embodiment.

FIG. 10 shows an overview of an apparatus depicting the major components of an illustrative embodiment.

Fig. 11a and 11b show cross-sectional views of an apparatus depicting the main components of an illustrative embodiment.

Fig. 12 depicts an illustrative embodiment with an optional block heater or cooler.

Fig. 13 depicts an illustrative embodiment with an optional block heater or cooler shown below the structure.

Fig. 14a, 14b, 14c, and 14d depict various illustrative embodiments of devices.

Detailed Description

In general, aspects of the present disclosure relate to evaporators produced using fine-scale microfabrication techniques for structures and heating elements. Microfabrication may include patterning, etching, deposition, implantation, and related processes on materials such as glass, metals, plastics, and crystalline materials such as silicon and silicon derivatives. The heating elements may comprise electronic circuits fabricated from electrical components including resistors, capacitors, transistors, logic elements, etc., which may also be fabricated on dedicated circuits and/or be made up of discrete components in any combination.

One or more embodiments described herein may provide well-controlled heating, thereby minimizing the effect of the liquid becoming overheated, thereby minimizing undesired chemical reactions that produce undesired and/or harmful chemical reaction products.

One or more embodiments described herein may provide evaporation devices that are manufactured in a highly controlled manner, thereby reducing significant cell-to-cell variation, and thus reducing performance variation.

One or more embodiments described herein may provide a thermodynamically efficient, small-volume evaporator.

The microfluidic vaporizers disclosed herein can be used to provide efficient vaporization of low volatility liquids for a wide range of applications, including flavor profiles, medical vaporization, vaporized drug delivery, chemical distillation, chemical reaction control, aromatics, waxes, scented waxes, air sterilization, theatrical vapor, nebulizers, aromatherapy, essential oils, personal vaporizers, chemical vapor or aerosol detector calibration devices, smoking articles, and electronic cigarettes.

evaporation devices are a general class of devices for generating a vapor or aerosol from a liquid. Evaporators have many applications, including but not limited to: flavor dispensing, medical vaporization, vaporized drug delivery, chemical distillation, chemical reaction control, aromatics, waxes, scented waxes, air sterilization, theatrical smoke, nebulizers, aromatherapy, essential oils, personal vaporizers, smoking articles, electronic cigarettes, and the like.

The present disclosure describes embodiments of microfabricated vaporization devices using modern microfabrication techniques, including photolithography, deposition and etching techniques. Such a technique can be advantageously applied to evaporator designs. For example, one embodiment may have micron-scale precision components. In other embodiments, the disclosed apparatus and methods may be compatible with injection molded plastic. In one embodiment, the evaporation apparatus and method may have a similar geometry from unit to unit. Further, an embodiment may be produced with high throughput and low cost.

The present application discloses embodiments that may provide the desired performance improvements. For example, in one embodiment, the micron-scale precision of the components allows for precise metering of vaporized material and precisely controlled temperature, which may eliminate areas of overheating that produce undesirable chemical reaction products. In other embodiments, the device may be designed to minimize parasitic heat transfer to the substrate, ambient environment, or interposer. In some embodiments, the device can be made very small, flat and highly portable. The micron-scale features may improve the thermodynamic efficiency of the apparatus and method, and may have minimal energy requirements. In yet another embodiment, the evaporation ports can be individually addressed and activated in a controlled manner so that a chemical reaction front or precise release of a particular chemical can be established based on the time and individual location within the array of evaporation ports.

FIG. 1 shows a schematic view of an evaporation unit for an illustrative embodiment. The unit includes a microfluidic device (not shown) for evaporation contained within a plastic housing, commonly referred to as an inserter body 204. Inserter body 204 may be mated with inserter retaining ring 202 via bolts 200. The electrical interconnect 206 may be used to transport electrical energy. Steam 102 may be emitted from the device.

Fig. 2a and 2b show exploded views of the embodiment. The inserter body 204 and the inserter retaining ring 202 are in communication with the evaporation structure 100. The evaporation structure 100 may be constituted by a microfluidic chip. The vapor region 208 communicates with the structure 100 and allows vapor to emanate from the microfluidic device structure 100. The electrical interconnect 206 is in electrical communication with the microfluidic device structure 100.

In one embodiment, the inserter body 204 is constructed of injection molded plastic and is designed to facilitate assembly. In other embodiments, the interposer body 204 may be 3D printed, machined, and may be fabricated from a wide selection of plastics, metals, fiberglass, composites, ceramics, or other structural materials.

The electrical interconnect 206 allows the device to be connected to an electronic control unit (not shown). In one embodiment, the electrical interconnect may be formed from conductive tape, flat wire, wire bonds, bump bonds, solder, or other connection processes.

in one illustrative embodiment, the overall dimensions of the plastic housing may be nominally 4mm by 6mm by 12 mm. In other embodiments, the plastic housing may range in size from less than 0.1mm to greater than 100mm and may contain one or more microfluidic devices.

FIG. 3 shows a cross-sectional view of an apparatus depicting various components of an embodiment. Fig. 3a is a side view, while fig. 3b is slightly inclined to show the top surface. An ambient environment 116 is above the structure 100. An evaporation port 110 is formed in the structure and is in fluid communication with a liquid source 112 and an ambient environment 116. The liquid source 112 is a region of the structure that is in fluid communication with a liquid reservoir (not shown) and the evaporator port region of the device. The heating element 108 is in thermal communication with the vaporization port 110 and is located on a structural region 114, and in some embodiments, the structural region 114 may be a thinned region of the structure. The heating element 108 is in electrical communication with the electrode lead 106. An evaporation cluster 104 is an area containing a set of evaporation ports 110 in close proximity to one or more evaporation ports 110. In some embodiments, the liquid source 112 may be a wax or other solid phase material that exists in a liquid phase near the vaporization ports 110 as a result of heating.

In the present context, thermal communication refers to the ability to easily transfer thermal energy from one area of a device to another area of the device by thermal conduction. In some embodiments, thermal communication occurs between two regions when the distance between the regions is significantly less than other dimensions in the device or the thermal conductivity of the material connecting the two regions is equal to or greater than the thermal conductivity of the material in the other regions of the device. In some embodiments, the heating element 108 may be in thermal communication with the vaporization port 110, as the lateral distance between the two components may be between 5 μm and 100 μm. In some embodiments, the distance between the heating element 108 and the vaporization port 110 may be in the range of 0.5 μm to 1 mm. This distance may be significantly smaller than other dimensions of the device. In illustrative embodiments, the depth of the structure 100 may be between 10 μm and 1000 μm, and the lateral dimension of the structure 100 may be in the range of between 1mm and 100mm or even greater.

Fig. 3a shows an illustrative embodiment of thin structured region 114, nominally 40 μm thick. In some embodiments, the thin structure region 114 may be in a range of 1 μm to 100 μm. In other embodiments, the thickness of the thin structure region 114 may vary from 1 μm to 1000 μm.

Fig. 4 shows an overview of an illustrative embodiment. An ambient environment 116 is above the structure 100. Vaporization ports 110 are formed in the structure 100 and are in fluid communication with the liquid source 112 area and the ambient environment 116. The heating element 108 is proximate to the vaporization port 110. In an illustrative embodiment, the heating element 108 may be located within 5-100 μm (or 0.5 μm to 1mm) of the vaporization port 110. In the illustrative embodiment, the heating element 108 is located within 0.5-1000 μm. The meniscus interface 118 defines a vapor and liquid interface. A thin structure region 114 may be formed in the structure 100. A contact region 140 can be formed between the liquid from the liquid source 112 and the thin structure region 114.

In some embodiments, thin structure region 114 may be adjacent to evaporation ports 110 and heating elements 108, which may minimize parasitic heat transfer to bulk structure 100. In some embodiments, the meniscus interface 118 separating the liquid in the evaporation port and the ambient environment may have a curvature capable of creating a pressure differential between the liquid source 112 and the ambient environment 116. In some embodiments, there is a significant contact surface area 140 between the low-profile structural region 114 and the liquid contained in the evaporation port 110 and the liquid source 112.

Fig. 4a depicts an illustrative embodiment where an optional block heater or cooler 120 may be positioned in thermal communication with the liquid source area 112 to control the body temperature of the liquid source 112.

Fig. 4b depicts an illustrative embodiment in which structure 100 is bonded to thin structure region 114 with structure bonds 122.

FIG. 4c shows an overview of the apparatus depicting various components of another illustrative embodiment. An ambient environment 116 is above the structure. An evaporation port 110 is formed in the structure 100 and is in fluid communication with a liquid source 112 and an ambient environment 116. Heating element 108 is in thermal communication with vaporization port 110 and is located on thin structural area 114. In one embodiment, the particles or beads 130 form a wicking structure that is located in all or a portion of the liquid source region 112 and also optionally in the evaporation port 110, and at least in a region adjacent to the evaporation port 110. In one embodiment, the particles or beads 130 may be hydrophilic. In one embodiment, the particles or beads 130 may be hydrophobic, or may be a hydrophilic/hydrophobic combination. In one embodiment, the hydrophilic particles or beads 130 may be formed of glass or other material. In one embodiment, the particles or beads 130 may optionally be sintered 132 or bonded together by some other means. In one embodiment, the particles or beads form small interstitial regions 138 that enhance the effect of the hydrophilic or hydrophobic surface properties of the beads or particles 130. In one embodiment, the size of the particles or beads 130 may be in the range of 10 nanometers to 10 millimeters. In one embodiment, the size of the particles or beads may be in the range of 1 micron to 1 millimeter. In one embodiment, the size range of the particles or beads 130 may be in the range of 10 microns to 300 microns.

Fig. 5 shows a top view of an apparatus depicting some of the major components of an embodiment. An evaporation port 110 is formed in the structure 100 and is in fluid communication with a liquid source region 112 and an ambient environment 116. The heating element is in thermal communication with the evaporation port 110 and is located on the low profile structural area 114. In one embodiment, the heating element 108 is a thin film resistive heating element. In one embodiment, the thin film heating elements are configured in three parallel circuits that further form a parallel circuit around each evaporation port.

FIG. 5 shows a detailed view of one such exemplary embodiment, wherein a single evaporation cluster 104 has a lateral dimension of approximately 900 μm and contains seven evaporation ports 110 having lateral dimensions of 60 μm-150 μm and a heating element 108 in thermal communication with the evaporation ports 110 such that heat generated by the heating element 108 is transferred into the area of the evaporation ports 110 in contact with the fluid 112 and the contact area 140. In illustrative embodiments, the lateral dimension of the evaporation ports may be in the range of 10 μm to 300 μm, while in other embodiments, the lateral dimension of the evaporation ports may be in the range of 1 μm to 1000 μm. In an illustrative embodiment, the lateral dimension of the evaporation clusters may be in the range of 10 μm to 100 mm. In an illustrative embodiment, the lateral dimension of the evaporation clusters may be in the range of 100 μm to 10 mm.

The width of the heating element 108 may optionally be configured to have varying widths and thicknesses, or to vary the material to produce a desired joule heating profile. In some embodiments, the desired heating profile may be selected to provide uniform evaporation of the working fluid while avoiding excessive heating from undesirable hot spots. In some embodiments, 0.01 to 500 watts of heat may be delivered into the fluid 112 to produce the steam 102. In other embodiments, 1 to 50 watts of heat may be delivered into the fluid 112 to produce the steam 102.

In some demonstrative embodiments, a hierarchy of resistive heating elements connected in parallel (as shown in fig. 5) may have certain advantages. For example, the resistance of a metal may increase with increasing temperature. Thus, if one element of the parallel circuit has a higher temperature than another element of the parallel circuit, that element may have a higher resistance and force more current through the low temperature element, thereby increasing the joule heating generated by the lower temperature element. In some embodiments, parallel-connected resistive heating elements may facilitate thermal regulation, which facilitates mitigating localized thermal hot spots.

Fig. 6a and 6b show an overview of a single microfluidic evaporation device structure 100. In the illustrative embodiment, a single device structure 100 contains eighteen evaporation clusters 104, and each cluster 104 contains seven evaporation ports 110, so for the exemplary embodiment, there are a total of 18 × 7-126 evaporation ports 110. In one exemplary embodiment shown in fig. 6a, two evaporation clusters 104 are connected by electrode leads 106 in series with nine parallel circuits. In another exemplary embodiment shown in fig. 6b, three evaporation clusters 104 are connected by electrode leads 106 in series with nine parallel circuits.

In other exemplary embodiments, the clusters may be connected in various series and/or parallel configurations, individually addressable, or other electrical wiring schemes. In an exemplary embodiment, the microfluidic device structure 100 has lateral dimensions of 4mm by 10mm and a thickness of 0.3 mm. In one exemplary embodiment, the microfluidic chip is fabricated from glass, but for other embodiments it may be fabricated from plastic, silicon, titanium, metal, ceramic, PDMS, polymer, fiberglass, composite, or other materials.

Q ═ V may be used²the term/R describes joule heating from a resistive element, where Q is the joule heating power, V is the voltage drop across the resistive element, and R is the resistance of the element. As the temperature increases, the resistance of the metal increases. If the voltage drop is constant, the amount of joule heating decreases as the temperature increases. Thus, in one embodiment, it may be advantageous to have a parallel circuit. If one branch of the parallel circuit has a higher temperature than the other branch of the circuit, the branch with the higher temperature will have a higher resistance and will therefore produce less joule heating. In embodiments having parallel resistive heaters, the various branches of the circuit may have self-regulating properties, which may help regulate joule heating, which may help maintain a more uniform temperature than non-uniformities that may occur using non-parallel circuit configurations.

in some embodiments, the parallel resistive heaters may be configured to have different resistances in each branch. In some embodiments, the resistance of the heating element may be modified by using different materials, different depths, different lengths, and/or different widths. In some embodiments, the individual branches of the parallel resistance heater may have different resistances, which may be optimized to produce a desired and well-controlled temperature profile. In some embodiments, a uniform temperature distribution may be desirable. In some embodiments, a non-uniform temperature distribution may be desirable.

In some embodiments, the staged combination of parallel resistive heating elements 108 may be judiciously selected to provide a desired heating profile and a self-regulating heating element.

Fig. 7a shows an example of a micro-fabrication process flow for device fabrication of an embodiment, which consists of five processing steps using a single structure. In an illustrative embodiment, structure 100 may be fabricated from a 300 μm thick glass substrate of Schott (D263T-eco, AF32-eco, or MEMPax). The glass substrate may be formed of various materials and has a thickness ranging from 1 μm to 10 mm. The photoresist may be patterned and metals (e.g., titanium and platinum) may be deposited for the electrode leads and heating elements (step 1-heater metal deposition 700). After photoresist and metal stripping, a hard mask film (e.g., chrome/gold, aluminum, or amorphous silicon) may be deposited on both sides of the substrate (step 2 — hard mask deposition 701). At the backside, the photoresist may be patterned and the hard mask may be etched (wet or dry), followed by an optional wet etch of the glass to about half the substrate thickness (step 3 — backside hard mask and glass etch 702). In the front, the vaporization port 110 may be patterned to be in close proximity to the heater element 108 (which may be in the range between 5 μm to 100 μm or 0.5 μm to 1mm) and the hard mask may be etched, followed by an optional glass wet etch. At the same time, the backside may optionally be further etched, as it may optionally be exposed, and vias (or through-holes) may be created (step 4 — top side hard mask and glass etch 703). This may place the evaporation port 110 in fluid communication with the liquid source 112 and the ambient environment 116. Finally, the hard mask may be removed from both sides, and then the substrate may be diced (step 5 — hard mask removal 704).

Some embodiments of evaporation devices may be fabricated using various nano-fabrication and micro-fabrication equipment. The fabrication may include a number of deposition tools, such as electron beam deposition which may be used for heating elements and Plasma Enhanced Chemical Vapor Deposition (PECVD) which may be used for depositing hard masks. In some embodiments, the wet chemistry station may be used for various etching chemistries, including hydrofluoric acid etching of glass. Dry etching may also be used for isotropic etching in certain materials, such as inductively coupled plasma reactive ion etching (ICP-RIE). Furthermore, in some embodiments, a backside-alignable lithographic mask aligner (such as SUSS MA-6) may be used to pattern and align features from front to back.

Fig. 7b shows an illustration of a micro-fabrication process flow for device fabrication for the illustrative embodiment shown in fig. 4b, which includes six processing steps using structural element 100 and thin structure region 114 (i.e., two initially separate structures). This embodiment may be extended to two or more (i.e., multiple) structures that may be joined using structure bonds 122 (shown in FIG. 4 b) using one or more joining techniques.

The manufacturing process may use a glass substrate 100 μm, 300 μm, or even 500 μm thick to form the structure 100. Embodiments may use a 1 μm to 10mm thick substrate for the thin structured region 114 (shown in fig. 4 b), and the substrate may comprise various materials such as glass, titanium, aluminum, sapphire, silicon carbide, diamond, ceramic, metal, silicon, and the like.

Two different thicknesses of substrate may be used. For example, one substrate may be a 100 μm (i.e., relatively thin) substrate and the other substrate may be a 300 μm (i.e., relatively thick) substrate, which may allow for significant flexibility in feature size during an alternative wet etch process. Referring to FIG. 7B, a 100 μm thick substrate may be patterned with photoresist and metal for the heating elements may be deposited (step 1-heater metal deposition 710). Additional metal deposition steps may optionally be used for the electrode leads. For example, in one embodiment, gold contacts may optionally be patterned at the chip connections.

In one embodiment, after photoresist and metal stripping, hard mask films may be deposited on both sides of the thin substrate (step 2 — hard mask deposition 711) and on the thick substrate. Photoresist may be patterned on both sides of the substrate to expose areas adjacent to the heating elements on the thin substrate and the thick substrate. The hard mask may be etched and then the substrate etched to half the thickness on each side of the substrate to form through holes (i.e., through holes through the chip) (step 3-hard mask and substrate etch 712), which may provide fluid communication for the evaporation port 110 with the liquid source 112 and with the ambient environment 116.

In this embodiment, the hard mask may then be removed from both sides of the substrate (step 4 — hard mask removal 713). The adhesive layer may be optionally deposited on the back surface of the thin substrate, the upper side of the thick substrate, or both, or neither, depending on the adhesive technique. Further, in some embodiments, appropriate cleaning and surface treatments may be applied to both substrates, and they may be bonded together using various well-known bonding techniques (step 5-adhesive layer deposition and wafer bonding 714). In some embodiments, the bonded assembly may then be cut into smaller individual units (step 6 — bonded assembly 715).

FIG. 8 shows a flow diagram depicting a method of an embodiment, the method comprising: liquid is directed from a liquid source to evaporation port 801 and the liquid in the evaporation port is heated using a heating element (which may be between 5 μm and 100 μm or between 0.5 μm and 1mm) located near the evaporation port to evaporate the liquid 802. In one embodiment, the vaporized liquid is released from the vaporization port into the ambient environment so that the fluid is transported 803 through the depth of the structure. In some embodiments, the lateral dimension of the evaporation port is in the range of 10 μm to 300 μm. In other embodiments, the lateral dimension of the evaporation port is in the range of 1-1000 μm. The liquid may be introduced into the liquid source by placing the liquid directly into the liquid source or by an optional pump or an optional wicking structure, wherein the liquid may be delivered to the liquid source by capillary action. In one embodiment, electrical energy may be applied to the heating element, and the heating element may be heated by joule heating (i.e., resistive heating). Thermal energy from the heating element can then be transferred into the thin structure region adjacent the evaporation port and the liquid source. The heat can then be conducted locally into the liquid to heat the liquid to the optimal evaporation temperature. The temperature may be well controlled so that the liquid is heated sufficiently for evaporation, but does not reach an undesirably high temperature that may cause undesirable chemical reactions or drying out of the evaporation ports. Furthermore, by controlling the electrical energy of the heating element, the evaporation rate or the total evaporation quality can be accurately controlled. In some embodiments, the amount of electrical energy may be optionally varied and optimized for a particular application. In other embodiments, the electrical waveform may be a sine wave, a square wave, or other waveform, which may be optimized for a particular application. In other embodiments, the waveform may pulse and cause evaporation, aerosol of droplets, or jets, and may reduce parasitic heat losses, thereby improving thermodynamic efficiency.

Fig. 9 refers to an illustrative embodiment in which liquid flows from the liquid source 112 area into the evaporation port 110 and then evaporates through the meniscus interface 118 into the ambient environment 116. In some embodiments, the liquid may be transported from one side (e.g., the back side) of the microfluidic device structure 100, evaporate through the meniscus interface 118 and release vapor from another side (e.g., the front side) of the microfluidic device structure 100, such that the fluid is transported through the depth of the structure (i.e., through the via or through hole). In these embodiments, the ability of liquid to travel through the device is made possible by the evaporation port 110 being in fluid communication with the liquid source 112 and the ambient environment 116. Arrows 134 indicate continuous fluid movement from one side of the structure to the other side of the structure. White arrows 134 indicate continuous fluid movement of liquid through the liquid source 112 to the evaporation ports 110. The black arrows 134 represent the continuous fluid movement of vapor from the evaporation port 110 to the ambient environment 116. The ability to transport fluid through the depth of the structure may make the evaporation process more energy efficient. In some embodiments, the ability of the fluid to be delivered through the depth of the structure may reduce or even prevent drying out and provide continuous fluid movement. In some embodiments, this may allow, for example, to addThe thermal element 108 is placed in close proximity (e.g., within 0.5 μm to 1000 μm or 5 μm to 100 μm) to the evaporation port 110 to facilitate the desired thermal communication with the meniscus interface 118 where the phase change occurs. This may significantly reduce the distance heat must be transferred into the liquid during evaporation compared to other evaporator devices, and may allow the heating element 108 to operate at lower temperatures. This can be particularly critical because most liquids have low thermal conductivity (e.g., water has a thermal conductivity of about k at room temperature)_w0.58W/(mK), and the thermal conductivity of glycerol is about k_w0.29W/(mK)). The efficient design of these embodiments may also reduce the maximum temperature to which the liquid must be exposed during evaporation. Furthermore, in some embodiments, a more efficient design of liquid flow through the microfluidic device may significantly reduce drying out of the liquid in the evaporation ports 110, thereby providing consistent and superior performance.

Fig. 9 refers to an illustrative embodiment where there is a significant contact surface area 140 between the thin structure area 114 and the liquid contained in the evaporation port 110 and liquid source area 112. Since liquids can have low thermal conductivity, it is important to have a large contact area 140 so that heat can be easily transferred from the thin structured area 114 to the liquid. In some embodiments, the low-profile structure region 114 can reduce the distance that heat can transfer from the heating element 108 through the low-profile structure region 114 before reaching the contact region 140 between the low-profile structure region 114 and the liquid source region 112 and the liquid in the evaporation port 110. In some embodiments, it may be important to have a minimum distance to transfer heat through the thin feature region 114, since glass has about k_gLow thermal conductivity of 1.05W/(mK). Other materials, such as metals, silicon, and the like, provide greater thermal conductivity, e.g., silicon has a thermal conductivity of approximately k_si130W/(mK). However, in many embodiments, for thermodynamic efficiency, it is important to focus the thermal energy near the evaporation ports, thus minimizing the heat transfer to the bulk substrate and the surrounding environment. In some embodiments, the thermal energy is substantially confined to the evaporation clusters 104. In some embodiments, the size of the evaporation cluster 104 may be nominally 1 mm. In some implementationsIn an example, the size of the evaporation clusters 104 may range from 100 μm to 10 mm. In some embodiments, the size of the evaporation clusters 104 may range from 10 μm to 100 mm. In many of these embodiments, it is advantageous to use a low thermal conductivity material such as, but not limited to, glass, plastic, polymer, fiberglass, composite, or ceramic, etc. In many of these embodiments, the thin structure region 114 in combination with the low thermal conductivity material may help minimize parasitic heat transfer losses to the bulk structure 100 and the ambient environment 116. In other embodiments, the use of optimized electrical waveforms may help to reduce parasitic heat transfer losses to the bulk structure 100 and the ambient environment 116.

In some embodiments, the glass has many characteristics that make it a suitable structural material for the evaporation device. For example, glass can be made very durable, can be provided in many geometric forms (including thin wafers), can be machined, can be custom blow molded, shaped or molded, is widely and commercially available, can be purchased at a reasonable price, can be wet etched, can have low electrical conductivity, can have low thermal conductivity, can be made hydrophilic by a suitable cleaning process, can be made hydrophobic by judiciously chosen surface coatings, can be treated with well-known surface chemistries, can be chemically inert, can be aggressively stripped of organic materials than fish solutions, can be mechanically stable below the glass transition temperature, can be deposited for electrode leads and heating elements, or can be bonded to itself or other materials.

In some embodiments, glass may be selected as a structural material for environmental, toxicity, or health reasons. In some embodiments, the electrode leads 116 and the heating element 108 may be formed from a deposition of platinum and titanium. Many other materials may be used for electrode and heating element deposition (such as carbon, gold, silver, nickel, aluminum, etc.). In some embodiments, platinum may be used as the electrode lead and the resistive heating element (via joule heating), and may also be used as a Resistive Thermal Device (RTD) for measuring the approximate temperature of the heating element. The resistance of platinum and many other metals and other materials is a function of temperature and can be used to determine the approximate temperature of the heating element. In some embodiments, the electrical control circuit may be used for feedback control of the evaporation device to maintain a constant operating temperature or constant operating power setting, or a time profile of the operating temperature or operating power, or may be some arbitrary operating time profile tailored to a particular application. Other metals and other materials may be used as RTDs for the vaporization device. However, in some embodiments, platinum may be a suitable material. In these embodiments, titanium may be a suitable bonding material to provide adhesion between the glass substrate and the platinum or other metal deposited film. Other adhesive materials may also be used.

In some embodiments, the heating element 108 in combination with the continuous fluid motion provides stable and uniform heating of the fluid, which may keep the fluid from attaining undesirably high temperatures that may cause undesirable chemical byproducts, or may burn, partially burn, or char the liquid and the microfluidic structure 100. In some embodiments, the continuous fluid movement may provide stable operation that may allow the device to function continuously for an indefinite period of time while minimizing potential undesirable consequences such as drying of the liquid, undesirable chemical byproducts, liquid charring or burning or device charring or burning.

In some embodiments, evaporation may occur over discrete time periods ranging from milliseconds to tens of seconds or longer. In some embodiments, evaporation may occur over a discrete period of time of a few milliseconds to tens of seconds or more to provide accurate delivery of vapor mass for accurate metering.

FIG. 10 shows an overview of an apparatus depicting various components of an illustrative embodiment. An ambient environment 116 is above the structure 100. An evaporation port 110 is formed in the structure 100 and is in fluid communication with a liquid source region 112 and an ambient environment 116. Heating element 108 is in thermal communication with vaporization port 110 and is located on thin structural area 114. White line 136 represents the profile at constant temperature. In some embodiments, the thin structured region 114 helps to confine the thermal energy substantially within the evaporation clusters 104 and within the vicinity of the heating elements 108 and evaporation ports 110, thereby reducing heat loss to the bulk structure 100.

In some embodiments, there is a significant contact surface area 140 between the low-profile structural region 114 and the liquid contained in the evaporation port 110 and the liquid source 112. Since the liquid may have a low thermal conductivity, it is important to have a large contact area 140 so that heat can be easily transferred from the thin structured area 114 to the liquid. In some embodiments, the low-profile structure region 114 can reduce the distance that heat can transfer from the heating element 108 through the low-profile structure region 114 before reaching the contact region 140 between the low-profile structure region 114 and the liquid source region 112 and the liquid in the evaporation port 110. In some embodiments, since glass has about k_gA low thermal conductivity of 1.05W/(mK) may be desirable to have a minimum distance to transfer heat through the thin structure region 114. Other materials, such as metals, silicon, and the like, provide greater thermal conductivity, e.g., silicon has a thermal conductivity of approximately k_si130W/(mK). However, in many embodiments, for thermodynamic efficiency, it is important to keep the thermal energy substantially focused within the evaporation clusters 104 and in close proximity to the evaporation ports 110, thus minimizing the heat transfer to the bulk substrate 100 and the ambient environment 116. In many of these embodiments, it may be advantageous to use a low thermal conductivity material, such as glass, plastic, polymer, fiberglass, composite, or ceramic, etc. In many of these embodiments, the thin structured region 114 in combination with the low thermal conductivity material may help minimize parasitic heat transfer losses to the bulk substrate 100 and the ambient environment 116. In other embodiments, the use of optimized electrical waveforms may help reduce parasitic heat transfer losses to bulk substrate 100 and ambient environment 116.

11a and 11b show an overview of an apparatus depicting various components of an illustrative embodiment. An ambient environment 116 is above the structure 100. An evaporation port 110 is formed in the structure 100 and is in fluid communication with a liquid source region 112 and an ambient environment 116. Heating element 108 is in thermal communication with vaporization port 110 and is located on thin structural area 114.

Fig. 11a shows an illustrative embodiment in which the thin structure region 114 is in an undeflected state, which may occur when the device is not energized. In one embodiment, the heating element 108 may be energized and generate thermal energy, which may increase the temperature in the vicinity of the heating element 108. The thin structure region 114 proximate the heating element 108 may thermally expand due to the increase in temperature, which may cause thermal stress and/or strain in the thin structure region 114 and the resistive heating element 108. In some embodiments, the primary stress is desirably less than 10-20 MPa. In some embodiments, the primary stress is desirably less than 70 MPa.

Fig. 11b shows an illustrative embodiment in which the thin structure region 114 deflects due to thermal expansion when the heating element 108 is activated. In the illustrative embodiment, thin structure region 114 may help identify thermal energy near heating element 108, which may help minimize thermal expansion of the bulk structure, and may help reduce thermal stress and strain in thin structure region 114. In some embodiments, the primary stress is desirably less than 10-20 MPa. In some embodiments, the primary stress is desirably less than 70 MPa.

In one embodiment, the thin structured region 114 may allow for thermal deflection and may help reduce thermal stress. Mechanical stiffness and h of structural beams³And proportionally, where h is the thickness of the structural beam. In some embodiments, the optional low profile structural region 114 may be sufficiently thin such that it may have a relatively low mechanical stiffness that may allow the low profile structural region 114 to deflect with sufficiently low stress when the heating element 108 is energized. In some embodiments, the primary stress is desirably less than 10-20 MPa. In some embodiments, the primary stress is desirably less than 70 MPa.

In one embodiment, the heating element 108 may be constructed of a metal having a high coefficient of thermal expansion compared to the structural material. As shown in fig. 11b, the thin structure region 114 may deflect and create a stain on the top surface that is well matched to the thermally induced strain of the heating element 108 material, such that stress between the heating element 108 and the thin structure region 114 may be significantly reduced. In some embodiments, the primary stress is desirably less than 10-20 MPa. In some embodiments, the primary stress is desirably less than 70 MPa.

FIG. 12 shows an overview of an apparatus depicting various components of another illustrative embodiment. In this embodiment, an optional seal 124 may be located between the liquid in the evaporation port 110 and the ambient environment 116. The sealing member 124 may be made of a thermally responsive wax. This may provide a seal that encloses the liquid during storage, and the optional seal 124 may then be evaporated to activate the evaporation device. The optional seal 124 may be used to extend shelf life prior to first use, or between uses. In some embodiments, the sealing material may be incorporated into a liquid to provide a self-sealing mechanism between uses or between evaporation processes. The optional seal 124 may be made of many different materials, not just the case of the exemplary wax. In some embodiments, the seal 124 may be constructed of a suitable sealing material that is solid at room temperature, but melts, sublimes, recedes, or clears from the evaporation port 110 when the evaporator is active. In some embodiments, the liquid source region 112 may contain a low volatility liquid, and an optional seal may not be necessary or may not be desirable. In some embodiments, the ambient environment 116 may be above the structure. The evaporation ports 110 formed in the structure 100 may be in fluid communication with the liquid source area 112, but may be optionally separated from the ambient environment by an optional seal 124. The heating element 108 may be proximate to the evaporation port 110 and located on the low profile structural area 114. In some embodiments, the heating element 108 is located within 0.5-1000 μm of the vaporization port 110. In some embodiments, the heating element 108 is located within 5 μm-100 μm of the vaporization port 110. In some embodiments, the optional seal 124 may evaporate and allow liquid in the evaporation port 110 to be in fluid communication with the ambient environment 116. An optional bulk heater or cooler 120 may be located below the structure 100. This may provide heat that may cause other solid phase materials to become liquid, or may increase the temperature of the entire liquid so that less thermal energy is required by the heating element 108. The optional block heater or cooler 120 may increase or decrease the overall temperature of the entire liquid, thereby allowing control of the volatility of the liquid prior to undergoing evaporation in the evaporation port 110.

Fig. 13 shows a schematic view of another embodiment where the liquid source area 112 is adjacent to the thin structure area 114. The ambient environment 116 is over the thin structured area 114. An evaporation port 110 is formed in the structure 100 and is in fluid communication with a liquid source 112 and an ambient environment 116. Heating element 108 is in thermal communication with vaporization port 110 and is located on thin structural area 114. An optional block heater or cooler 120 is shown below the structure 100.

Fig. 14a shows an illustrative embodiment in which an optional protective layer 126 surrounds the heating element 108. The protective layer 126 may be deposited of silicon dioxide, amorphous silicon, silicon nitride, or other materials. In some embodiments, the protective layer 126 may protect the heating element 108 from delamination due to differences in thermal expansion between the heating element 108 material and the underlying structure 100 material. In some embodiments, the protective layer 126 may serve as a chemical and/or electrical barrier between the heating element 108 and the ambient environment 116. In some embodiments, the protective layer 126 is located in close proximity to the heating element 108. In some embodiments, the protective layer 126 is located in the range of 0.5 μm to 1mm of the heating element 108. In some embodiments, the protective layer 126 substantially covers the structure 100.

Fig. 14b shows an embodiment in which an optional surface coating 128 is applied on the outside of the structure 100 and is located near the evaporation ports 110. In some embodiments, it may be desirable to prevent the coating from coating the walls of the evaporation port 110. Thus, when the coating is deposited, the evaporator ports may be masked during the coating process. In one embodiment, the optional surface coating 126 is a hydrophobic coating. In another embodiment, the optional surface coating 126 is a hydrophilic coating. In another embodiment, the optional surface coating 126 is a combination of hydrophobic and hydrophilic coatings. In one embodiment, the hydrophobic coating may be comprised of a fluoropolymer or other material. In one embodiment, the optional surface coating 126 may be comprised of a chemical monolayer. In one embodiment, the hydrophobic coating may repel the hydrophilic liquid and may minimize the hydrophilic liquid to prevent wetting of the exterior of the structure. In one embodiment, the hydrophilic coating may repel the hydrophobic liquid and may minimize the hydrophobic liquid to prevent wetting of the exterior of the structure.

Fig. 14c shows an embodiment in which an optional protective layer 126 surrounds the heating element 108, wherein an optional surface coating 128 is applied on the optional protective layer 126 surrounding the heating element 108 and is located adjacent to the evaporation port 110 but optionally not on the evaporation port 110. The protective layer 126 may be deposited silicon dioxide, amorphous silicon, or other materials. In some embodiments, the protective layer 126 may protect the heating element 108 from delamination due to differences in thermal expansion between the heating element 108 material and the underlying structure 100 material. In some embodiments, the protective layer 126 may serve as a chemical and/or electrical barrier between the heating element 108 and the ambient environment 116. In some embodiments, the protective layer 126 is located in close proximity to the heating element 108. In some embodiments, the protective layer 126 is located in the range of 0.5 μm to 1mm of the heating element 108. In some embodiments, the protective layer 126 substantially covers the structure 100. In one embodiment, the surface coating 128 is a hydrophobic coating. In another embodiment, the surface coating 128 is a hydrophilic coating. In another embodiment, the surface coating is a combination of hydrophobic and hydrophilic coatings. In one embodiment, the optional hydrophobic surface coating 128 may be comprised of a fluoropolymer or other material. In one embodiment, the optional hydrophobic surface coating 128 may repel hydrophilic liquids and may minimize hydrophilic liquids to prevent wetting of the exterior of the structure 100. In one embodiment, the hydrophilic surface coating 128 may repel hydrophobic liquids and may minimize hydrophobic liquids to prevent wetting of the exterior of the structure 100.

Fig. 14d shows an embodiment in which an optional surface coating 128 is applied on the interior of the structure 100 and is located near the evaporation ports 110 and the liquid source area 112. In the illustrative embodiment, the optional surface coating 126 is a hydrophobic coating. The hydrophobic coating may be adapted to be wetted with a hydrophobic liquid. In another embodiment, the optional surface coating 126 is a hydrophilic coating such that a hydrophilic liquid wets the hydrophilic coating. In another embodiment, the optional surface coating 126 is a combination of hydrophobic and hydrophilic coatings. In one embodiment, the hydrophobic coating may be comprised of a fluoropolymer or other material. In one embodiment, the optional surface coating 126 may be comprised of a chemical monolayer. In one embodiment, the hydrophobic coating may repel the hydrophilic liquid and may minimize the hydrophilic liquid to prevent wetting of the interior of structure 100 and evaporation port 110, while allowing the hydrophobic liquid to wet the interior of structure 100 and evaporation port 110. In one embodiment, the hydrophilic coating may repel the hydrophobic liquid and may minimize the hydrophobic liquid to prevent wetting of the interior of the structure 100 and the evaporation port 110.

Fig. 14d shows an exemplary embodiment with an alternative structural heater 210 that may be used to apply thermal energy to the structure. The alternative structural heater may be a thin film resistive heating element or other type of heating element. The solid material 212 may be heated using thermal energy from the structure. The solid material 212 may be a solid wax or wax-like substance, or any other type of solid material. The solid material 212 is in thermal communication with the structure 100. By appropriate application of thermal energy from the structure 100, the solid material 212 may be controllably melted into a liquid that may occupy the liquid source area 112. The optional surface coating 128 may be selected such that liquid occupying the liquid source region 112 may wet the structure 100 and the evaporation ports 110. When the heating element 108 is energized, liquid from the liquid source 112 may be vaporized in the vaporization port 110 such that the vapor may be discharged into the ambient environment 116.

The embodiments described herein are exemplary. Modifications, rearrangements, substitutions of procedures, materials, etc., may be made to these embodiments and still be encompassed within the teachings set forth herein.

Conditional language, such as "may," "can," "e.g.," as used herein, is generally intended to convey that certain embodiments include but other embodiments do not include certain features, elements, and/or states unless expressly stated otherwise or otherwise understood in the context of the usage. Thus, such conditional language is not generally intended to imply any way that features, elements, and/or states are required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether such features, elements, and/or states are included or are to be performed in any particular embodiment. The terms "comprising," "including," "having," "involving," and the like, are synonymous and are inclusive in an open-ended manner and do not exclude additional elements, features, acts, operations, and the like. Furthermore, the term "or" is used in its inclusive sense (and not its exclusive sense), so that when a list of elements is used, for example, to connect, the term "or" refers to one, some, or all of the elements in the list.

Unless otherwise expressly stated, separate language such as the phrase "X, Y or at least one of Z" is generally understood with the context to mean that an item, term, etc. can be X, Y or Z, or any combination thereof (e.g., X, Y and/or Z). Thus, such disjunctive language is generally not intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to be present.

The terms "about" or "approximately" and the like are synonymous and are used to indicate that the value modified by the term has an understood range associated therewith, which may range from ± 20%, ± 15%, ± 10%, ± 5% or ± 1%. The term "substantially" is used to indicate that a result (e.g., a measured value) is close to a target value, where "close" can mean, for example, that the result is within 80% of the value, within 90% of the value, within 95% of the value, or within 99% of the value.

Articles such as "a" and "an" should generally be construed to include one or more of the described items unless expressly stated otherwise. Thus, for example, an "apparatus configured as … …" is intended to include one or more of the recited apparatuses. Such one or more recited devices may also be collectively configured to perform the recited recitations. For example, "an element configured to execute narration A, B and C" may include a first element configured to execute narration a working with a second element configured to execute narration B and C.

While the above detailed description has shown, described, and pointed out novel features as applied to illustrative embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or method illustrated may be made without departing from the spirit of the disclosure. As will be recognized, certain embodiments described herein may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. An evaporation apparatus for placement in an ambient environment and for evaporating a liquid into the ambient environment, the evaporation apparatus comprising:

At least one liquid source;

At least one evaporation port formed in a structure, the evaporation port comprising a through hole having a lateral dimension ranging from 10 μm to 300 μm and which is in fluid communication with a source of liquid and an ambient environment, wherein fluid is transported from one side of the structure to another side of the structure through the through hole; and

At least one heating element in thermal communication with the at least one evaporation port.

2. The apparatus of claim 1, wherein fluid communication between the liquid source and the ambient environment occurs over an entire depth of the apparatus.

3. The apparatus of claim 2, wherein the structure comprises a thin structure region having a thickness varying from 1 μ ι η to 100 μ ι η, the at least one heating element is located on the thin structure region, and the thin structure region is adjacent to the at least one evaporation port and the at least one heating element.

4. The apparatus of claim 3, wherein a protective layer is formed on the structure surrounding the heating element.

5. The apparatus of claim 4, wherein the protective layer comprises deposited glass.

6. The apparatus of claim 3, wherein a surface coating is formed on the structure but is masked to prevent formation on the walls of the evaporation port.

7. The apparatus of claim 6, wherein the surface coating comprises a fluoropolymer.

8. the apparatus of claim 4, wherein a surface coating is formed on the structure but is masked to prevent formation on the walls of the evaporation port.

9. The device of claim 2, wherein at least one of a bead or particle wicking structure is located in one of the liquid source regions of the structure or within a port.

10. The apparatus of claim 9, wherein at least one of the beads or particles has a size of 10 to 300 μ ι η.

11. The apparatus of claim 10, wherein at least one of the beads or particles comprises a hydrophilic surface.

12. The apparatus of claim 11, wherein at least one of the beads or particles is sintered.

13. The apparatus of claim 12, wherein at least one of the beads or particles is comprised of glass.

14. The apparatus of claim 2, wherein the heating element is a thin film resistive heating element.

15. The apparatus of claim 14, wherein the resistance of the resistive heating element is varied to provide a controlled thermal profile.

16. The apparatus of claim 15, wherein the resistive heating elements are electrically connected in a combination of parallel and series.

17. A method of evaporating a liquid into an ambient environment, comprising:

Directing liquid from a liquid source to an evaporation port formed in a structure, wherein the evaporation port comprises a through hole having a lateral dimension from 10 μm to 300 μm;

Applying heat to the liquid in the evaporation port with at least one heating element positioned in thermal communication with the evaporation port; and

Releasing the vaporized liquid from the vaporization port into the ambient environment such that fluid is transported from one side of the structure to another side of the structure through the through-hole.

18. The method of claim 17, wherein during operation, liquid continuously flows from the liquid source to the evaporation port, changes from a liquid phase to a vapor, and the vapor continuously flows from the evaporation port into the ambient environment.

19. The method of claim 18, wherein a low profile structural area substantially confines thermal energy to the vicinity of the at least one heating element and at least one vaporization port.

20. The method of claim 19, wherein the thin structural region reduces thermally induced stresses occurring proximate the at least one heating element and the at least one evaporation port.